Mechanical coupling for torque transducer

In certain applications when the torque on shafts is to be measured, it is required, in addition to the requirement that the torque transducer should be attached so as to be rigid in the direction of rotation, that it should also be connected so as to have low axial and flexural rigidity, which is due to the fact that the shaft has a not insignificant axial movement and bending. Unless special measures are taken, such movements will have a manifestly negative influence on the torque measurement.

Another very important requirement in this connection is that the application of a torque transducer should not be allowed to extend the shaft between the drive source and the load object to any mentionable degree.

An application which requires a torsionally rigid coupling, which still has low axial and flexural rigidity, to obtain a good torque measurement is the attachment of the torque transducer for measurement of the torque in the crankshaft of a car engine between the engine and the gearbox.

The above-mentioned demands for attachment of the torque transducer have previously made it more or less impossible to measure the torque in crankshafts in immediate proximity to the driving motor.

The invention comprises a specially shaped mechanical coupling between a drive source and a load object which allows attachment of a torque device and makes possible torque measurement under the conditions resulting from the above-mentioned requirements.

Torque measurement in shafts can be performed by means of transducers based on different measurement principles, for example with the aid of strain gauges or with magnetoelastic methods. The torque measurement always takes place within a certain measuring zone or a certain measuring range on the shaft. Concentrically around the measuring zone are mounted torque-sensing or signal-transmitting devices with different designs depending on the measurement principle which will be used.

The coupling according to the invention can be used independently of which measurement principle will be used. As an example of an application, the coupling according to the accompanying figure may be used for torque measurement in the crankshaft of a car engine between the engine and the gearbox or the clutch. The figure also shows how, in principle, a torque-sensing or signal-transmitting device can be fixed in relation to the measuring zone of a shaft.

The coupling according to the invention comprises a relatively thin-walled tube which at one end is covered with a plate and which at its other end is provided with an outwardly-facing weak flange. Via holes in the flange, the coupling is bolted to the crankshaft. That part of the shaft which comprises the measuring zone, the transducer shaft, is fixed concentrically in the thin-walled tube to the plate.

The present invention can be more fully understood with reference to the accompanying drawing which is a cross-sectional view of a coupling according to the present invention, for a torque transducer.

The present invention relates to a combination including a drive source having an end portion with a recess formed therein, a mechanical coupling drivingly connected to the end portion, a transducer shaft drivingly connected to the mechanical coupling, a load object drivingly connected to the transducer shaft, and a signal transmitting device disposed adjacent the transducer shaft.

The mechanical coupling comprises a thin-walled tube having an inner end, an outer end, a cylindrical inner wall surface, and a cylindrical outer wall surface. The tube extends from the outer end inwardly into the recess. The outer end of the thin-walled tube includes an outwardly extending weak flange which is connected to the end portion of the drive source. The inner end of the thin-walled tube includes an inwardly extending plate portion which is in the shape of a flat ring-shaped plate or plate portion connected to the transducer shaft.

The plate portion has an inner wall defining a central opening therein for receiving the transducer shaft. The transducer shaft has an outer wall, a first end connected at the outer wall to the inner wall of the plate portion, and a second opposite end connected to the load object. The transducer shaft is spaced from and disposed within the thin-walled tube to define an annular space therebetween. Means are provided in the form of a bracket to support the signal transmitting device within the recess and the annular space with the signal transmitting device disposed radially outwardly of the transducer shaft.

An embodiment of the invention is clear from the accompanying figure. A crankshaft 1 is journalled in an engine block 3 by means of a crankshaft bearing 2. The end of the crankshaft extending from the engine block is provided with a hole 4 inside which the coupling is situated. As already mentioned, the coupling comprises the thin-walled tube 5 and the weak flange 6 in which holes 7, 8 are provided for securing the coupling to the crankshaft by screws. The other end of the tube is provided with the plate 9. Concentrically in the cylindrical tube and to the plate, the transducer shaft 10 is fixed. According to the figure, the plate 9 may be provided with a concentric hole adapted to the centering and fixing of the transducer shaft. The other end of the transducer shaft is connected, with the aid of a joint 11, to an automatic gearbox or the clutch or flywheel 12 of the vehicle. The joint may be designed in a number of different ways, for example as a polygon, splines, welded, shrinkage or keyway joint.

In one embodiment the mechanical coupling may be provided with a guide spindle 13 which concentrically extends from the transducer and the plate and which is journalled in some suitable way in the crankshaft.

The coupling may consist of an integrated design where the circular plate, the cylindrical tube and the weak flange are made in one piece, as shown in the figure, or consist of separately manufactured parts which are welded or otherwise fixed to each other.

To obtain a good measure of the torque, the signal-transmitting device should in some way be concentrically coupled to the transducer shaft. In an embodiment according to the figure, this is done by mounting the signal-transmitting device 14 on the transducer shaft by means of transducer bearings 15 and 16. The signal-transmitting device, which is stationary in relation to the rotating shafts, may suitably be fixed to the engine block 3 by means of a clamp 17.